As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased as an energy source for the mobile devices. Among them is a lithium secondary battery having high energy density and high discharge voltage, on which much research has been carried out and which is now commercially and widely used.
Depending upon the shape of a battery case, a secondary battery may be classified as a cylindrical battery having a jelly-roll mounted in a cylindrical metal container, a prismatic battery having a jelly-roll mounted in a prismatic metal container, or a pouch-shaped battery having a jelly-roll mounted in pouch-shaped case made of an aluminum laminate sheet.
Also, an electrode assembly mounted in the battery case is a power generating element, having a cathode/separator/anode stacking structure, which can be charged and discharged. The electrode assembly may be classified as a folding type electrode assembly (jelly-roll) constructed in a structure in which a long-sheet type cathode and a long-sheet type anode, to which active materials are applied, are wound while a separator is disposed between the cathode and the anode or a stacking type electrode assembly constructed in a structure in which pluralities of cathodes and anodes having a predetermined size are consecutively stacked while separators are disposed respectively between the cathodes and the anodes. The jelly-roll is preferred because the jelly-roll is easy to manufacture and has high energy density per weight.
The structure of a conventional representative cylindrical lithium secondary battery is typically illustrated in FIG. 1.
Referring to FIG. 1, a secondary battery 10 includes a cylindrical container 20, an electrode assembly 30 mounted in the container 20, and a cap assembly 40 coupled to the top of the container 20.
The electrode assembly 30 is constructed in a structure in which a cathode 31 and an anode 32 are wound in a jelly-roll shape while a separator 33 is interposed between the cathode 31 and the anode 32. To the cathode 31 is attached a cathode lead 34, which is connected to the cap assembly 40. To the anode 32 is attached an anode lead (not shown), which is connected to the bottom of the container 20.
The cap assembly 40 includes a top cap 41 constituting a cathode terminal, a positive temperature coefficient (PTC) element 42 for interrupting electric current through the great increase of battery resistance when the interior temperature of the battery increases, a bent safety member 43 for interrupting electric current or discharging gas when the interior pressure of the battery increases, a gasket 44 for electrically isolating the bent safety member 43, excluding a specific portion of the bent safety member 43, from a cap plate 45, and the cap plate 45 connected to the cathode lead 34, which is attached to the cathode 31. The cap assembly 40 is constructed in a structure in which the top cap 41, the PTC element 42, the bent safety member 43, the gasket 44, and the cap plate 45 are consecutively stacked.
Meanwhile, the jelly-roll type electrode assembly is constructed in a structure in which the anode is wound to constitute the outermost electrode layer, and a sealing tape for preventing the anode from unwinding is attached to the outside of the anode. In this state, the jelly-roll type electrode assembly is mounted in the metal container.
Generally, when the jelly-roll type electrode assembly is mounted in the metal container to constitute a battery, the anode lead is welded to an anode current collector of the electrode assembly, and the anode lead is also welded to the metal container. In this case, however, several problems occur. First, the electrode lead is added between a cathode current collector and the anode current collector, which consecutively form uniform contact interfaces. As a result, at least a portion of the anode current collector where the electrode lead is attached is bent. The portion of the anode current collector may be deformed as the jelly-roll repeatedly expands and contracts due to the continuous charge and discharge of the battery (J/R twist). Second, a space for the electrode lead is needed between the electrode assembly and the metal container, with the result that the size of the battery increases as compared with other batteries having the same capacity.
In order to solve the above-mentioned problems, Japanese Patent Application Publication No. 2001-196090 discloses a technology for achieving the direct connection with the metal container using a conductive tape as the sealing tape of the jelly-roll type electrode assembly. However, this technology has a disadvantage in that the conductive tape is separated from the container at the portion where the conductive tape and the container is in contact with each other, as the jelly-roll repeatedly expands and contracts due to the continuous charge and discharge of the battery, whereby a short circuit may occur. In order to solve the above-mentioned problem, the jelly-roll type electrode assembly may be constructed with a size almost corresponding to the inner diameter of the container. In this case, however, there is a great possibility that the outer separator and electrode will be damaged when the jelly-roll type electrode assembly is inserted into the metal container.
Therefore, there is a high necessity for a technology that is capable of preventing the jelly-roll from unwinding, during the assembly of the secondary battery including the jelly-roll type electrode assembly, and maintaining the stable connection between the conductive tape and the metal container when the jelly-roll repeatedly expands and contracts due to the continuous charge and discharge of the battery.